Liquid crystal display device

ABSTRACT

A liquid crystal display device of a vertical alignment mode is provided in which a quenching pattern, which is generated by such liquid crystal molecules whose in-plane component of the alignment directions under applied voltage is aligned along the cross nicole directions, is unrecognizable for a user. In the liquid crystal display device of a vertical alignment mode, a liquid crystal layer is has a defined value of d/p between 0.0021×(Vmax) 2 −0.0458×(Vmax)+0.65 and 0.0021×(Vmax) 2 −0.0458×(Vmax)+0.50, and a defined value of d·Δn/λ between −0.00026×(Vmax) 3 +0.016×(Vmax) 2 −0.2281×(Vmax)+2.124 and −0.00026×(Vmax) 3 +0.016×(Vmax) 2 −0.2281×(Vmax)+1.7603, where Vmax [V] is the maximum applied effective voltage applied to the liquid crystal layer.

FIELD OF THE INVENTION

[0001] The present invention relates to a liquid crystal display deviceemploying a vertically alignment mode.

BACKGROUND OF THE INVENTION

[0002] Conventionally, liquid crystal devices have been widely used as ascreen for word processors and computers, and recently have beenpervasive as a screen for televisions. Most of the liquid crystaldisplay devices employ a TN (Twisted Nematic) mode. However, the TN modeliquid crystal display device has problems that contrast decreases andtone characteristic inversion is likely to occur when viewed on anangle.

[0003] To improve a viewing angle characteristic in an angled direction,a liquid crystal display device employing a VA (Vertically Alignment)mode has come to receive attention in these years. For example, a VAmode liquid crystal display device is disclosed in U.S. Pat. No.6,384,889 (patented on May 7, 2002; hereinafter referred to asconventional example) corresponding to Japanese Laid-Open PatentApplication No. 2000-47251 (Tokukai 2000-47251; published on Feb. 18,2000). A liquid crystal cell of the VA mode liquid crystal device iscomposed of vertical alignment layers and a nematic liquid crystalhaving a negative dielectric anisotropy.

[0004] In the VA mode liquid crystal display device, liquid crystalmolecules are aligned in a vertical direction under no applied voltage.When linearly polarized light from a polarization plate enters theliquid crystal layer having the liquid crystal molecules in this state,the light leaves the liquid crystal layer as linearly polarized lightwithout changing the state of polarization, because the liquid crystallayer has almost no birefringence anisotropy. The linearly polarizedlight is then absorbed by a polarization plate located on the other sideof the liquid crystal layer. As a result, the liquid crystal displaydevice can produce black display.

[0005] On the other hand, when a voltage is applied, the liquid crystalmolecules in the liquid crystal layer are tilted according to theapplied voltage. Here, when the liquid crystal molecules are radiallyaligned as shown in the conventional example for example, the aligneddirection of the liquid crystal molecules continuously varies evenwithin a picture element region.

[0006] Further, among these types of liquid crystal display devices,there has been a liquid crystal display device in which a chiral dopantis added to vary the alignment of the liquid crystal molecules in aspiral manner along the thickness direction of the liquid crystal layer,as in the normal twisted alignment. This reduces a dark field portion,thereby improving brightness of the liquid crystal device.

[0007] In the foregoing conventional example, (U.S. Patent No.6,384,889), as described in the first paragraph of EXAMPLE 7(corresponding to paragraph [0039] in Tokukai 2000-47251) for example, achiral dopant is added so that a chiral pitch of 18 [μm], which is aboutfour times the cell thickness, is obtained, and a twist angle is set tobe about 90 degrees under applied voltage. Under these conditions, aserious quenching pattern remains over a large area and with highintensity, resulting in decrease in transmission intensity and decreasein brightness.

[0008] Further, the liquid crystal display device disclosed in U.S.patent application Publication No. 0,036,740 (published on Mar. 28,2002) includes a structure in which liquid crystal has a twistedstructure for the stable alignment of the liquid crystal. However, thispublication does not have a notion of eliminating the quenching pattern,or improving the transmittance by eliminating the quenching pattern.Further, the publication does not disclose optimizing the quenchingpattern or transmittance.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a liquid crystaldisplay device of a vertical alignment mode having a high transmissionintensity, i.e., high brightness, the invention realizing the liquidcrystal display device (A) by reducing a quenching pattern, which isgenerated according to a relationship between (i) directions ofpolarization axes of two polarization plates which are arranged in across nicole manner and (ii) an alignment direction of liquid crystalmolecules under applied voltage, to such a degree as to be completelyunrecognizable for a user, and (B) by determining optical physicalproperty values that can maximize the transmission intensity.

[0010] In order to achieve the foregoing object, the present inventionprovides a liquid crystal display device which includes a firstsubstrate, a second substrate, and a liquid crystal layer between thefirst substrate and the second substrate, the liquid crystal layer beingvertically aligned when no voltage is applied across (i) a firstelectrode provided on the first substrate and (ii) a second electrodeprovided on the second substrate so as to face the first electrode viathe liquid crystal layer, the liquid crystal layer having a twistedstructure and being aligned parallel to the substrates when a voltage isapplied across the first electrode and the second electrode, whereby theliquid crystal display device has a defined value for d/p between0.0021×(Vmax)²−0.0458×(Vmax)+0.65 and 0.0021×(Vmax)²−0.0458×(Vmax)+0.50,and has a defined value for d·Δn/λ between−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.124 and−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+1.7603, where d/p is theratio of a thickness d of the liquid crystal layer with respect to thenatural twist pitch p of a liquid crystal, Vmax [V] is the maximumapplied effective voltage across the first electrode and the secondelectrode, and An is the refractive anisotropy of the liquid crystallayer.

[0011] With this arrangement, when no voltage is applied across thefirst and the second electrodes, the liquid crystal molecules in theliquid crystal layer are vertically aligned. This causes no birefringenteffect or optical rotatory effect, so that the light passes through theliquid crystal layer and leaves the liquid crystal layer almostunaffected. On the other hand, when a voltage is applied, the liquidcrystal layer assumes a twisted structure and the liquid crystalmolecules are aligned parallel to the substrates, thereby causing thebirefringent effect and optical rotatory effect. As a result, the stateof light that leaves the liquid crystal layer can be changed dependingon whether or not a voltage is applied, enabling the display state to bechanged in accordance with the voltage.

[0012] The inventors of the present invention have diligently worked ona liquid crystal display device of a vertical alignment mode (A) toreduce a quenching pattern, which is generated according to arelationship between (i) directions of polarization axes of polarizationplates which are arranged in a cross nicole manner and (ii) an alignmentdirection of liquid crystal molecules when a voltage is applied, to sucha degree as to be unrecognizable for a user, and (B) to determineoptical physical property values that can maximize the transmissionintensity. As a result, the inventors of the present invention haveaccomplished the present invention by finding that (1) the liquidcrystal molecules in the vicinity of the substrates remain verticallyaligned even under applied voltage by the pre-applied regulating forcesacting on the liquid crystal molecules, because the liquid crystalmolecules are vertically aligned under no applied voltage in the liquidcrystal display device of a vertical alignment mode, (2) the thicknessof a portion of the liquid crystal molecules where the birefringenteffect and optical rotatory effect are generated is accordingly thinnerthan the actual thickness of the liquid crystal layer, and (3) thethickness of this portion of the liquid crystal molecules varies inaccordance with an applied voltage.

[0013] Namely, in the liquid crystal display device of the presentinvention, the liquid crystal layer has defined values for d/p andd·Δn/λ that respectively fall in the foregoing ranges, i.e., the valuesaccording to the maximum applied effective voltage on the first andsecond electrodes, and that have been set by taking into account theinclined alignment of the liquid crystal molecules in the vicinity ofthe substrates under applied voltage. As a result, it is possible tosuppress the quenching pattern to a such degree as to be unrecognizablefor a user, thereby realizing a liquid crystal display device capable ofrealizing brighter display with higher display quality, compared with adevice in which the quenching pattern is recognized. Here, the quenchingpattern that can be reduced in the present invention is a quenchingpattern that generates on the electrodes within picture elements.

[0014] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 represents graphs showing (i) a numerical range of d/p and(ii) a numerical range of d·Δn/λ with respect to maximum effectivevoltage in accordance with one embodiment of the present invention.

[0016]FIG. 2 is a cross-sectional view schematically showing a main partof a liquid crystal display device under no applied voltage.

[0017]FIG. 3 is a top view of the liquid crystal display device viewedin a direction normal to the substrate.

[0018]FIG. 4 is a drawing of a liquid crystal cell of the liquid crystaldisplay device, schematically showing a state (ON initial state) wherethe alignment of liquid crystal molecules in a liquid crystal layerstarts changing in response to an applied voltage to the liquid crystallayer.

[0019]FIG. 5 is a drawing of the liquid crystal cell of the liquidcrystal display device, schematically showing a steady state where thealignment of liquid crystal molecules has changed in response to theapplied voltage to the liquid crystal layer.

[0020]FIG. 6 is a view schematically showing a relationship between anequipotential line and alignment of a liquid crystal molecule when theequipotential line is orthogonal to the axial direction of the liquidcrystal molecule.

[0021]FIG. 7 is a view schematically showing a relationship between anequipotential line and alignment of a liquid crystal molecule when theequipotential line is inclined with respect to the axial direction ofthe liquid crystal molecule.

[0022]FIG. 8 is a view illustrating a relationship between anequipotential line and alignment of liquid crystal molecules,schematically showing (a) a liquid crystal molecule aligned by anelectric field whose equipotential line is inclined with respect to theaxial direction of the liquid crystal molecule and (b) liquid crystalmolecules aligned by an electric field whose equipotential line isperpendicular to the axial direction of the liquid crystal molecules soas to conform to the liquid crystal molecule (a).

[0023]FIG. 9 is a view schematically showing a relationship between anequipotential line and alignment of liquid crystal molecules when anelectric field whose equipotential line forms continuous irregularitiesis applied.

[0024]FIG. 10 is a view schematically showing alignment directions ofthe liquid crystal molecules when the liquid crystal molecules areviewed in a direction normal to the substrate under no applied voltage.

[0025]FIG. 11 is a view schematically showing alignment directions ofthe liquid crystal molecules when the liquid crystal molecules areviewed in a direction normal to the substrate in the ON initial state.

[0026]FIG. 12 is a view schematically showing alignment directions ofthe liquid crystal molecules when the liquid crystal molecules areviewed in a direction normal to the substrate in the steady state.

[0027]FIG. 13 is a graph showing a relationship between areatransmission intensity and d·Δn/λ at each different value of d/p undermaximum applied effective voltage of 10 [V].

[0028]FIG. 14 is a graph showing a relationship between areatransmission intensity and d·Δn/λ at each different value of d/p undermaximum applied effective voltage of 6 [V].

[0029]FIG. 15 is a graph showing a relationship between areatransmission intensity and d·Δn/λ at each different value of d/p undermaximum applied effective voltage of 4 [V].

[0030]FIG. 16 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the counterelectrode in the liquid crystal display device, when pitch p=0.

[0031]FIG. 17 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the middle of the liquidcrystal layer in the liquid crystal display device, when pitch p=0.

[0032]FIG. 18 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the pictureelement electrode in the liquid crystal display device, when pitch p=0.

[0033]FIG. 19 is a diagram showing a transmission intensity distributionin the liquid crystal display device, when pitch p=0.

[0034]FIG. 20 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the counterelectrode in the liquid crystal display device, when d/p=0.13.

[0035]FIG. 21 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the middle of the liquidcrystal layer in the liquid crystal display device, when d/p=0.13.

[0036]FIG. 22 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the pictureelement electrode in the liquid crystal display device, when d/p=0.13.

[0037]FIG. 23 is a diagram showing a transmission intensity distributionin the liquid crystal display device, when d/p=0.13.

[0038]FIG. 24 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the counterelectrode in the liquid crystal display device, when d/p=0.38.

[0039]FIG. 25 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the middle of the liquidcrystal layer in the liquid crystal display device, when d/p=0.38.

[0040]FIG. 26 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the pictureelement electrode in the liquid crystal display device, when d/p=0.38.

[0041]FIG. 27 is a diagram showing a transmission intensity distributionin the liquid crystal display device, when d/p=0.38.

[0042]FIG. 28 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the counterelectrode in the liquid crystal display device, when d/p=0.48.

[0043]FIG. 29 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the middle of the liquidcrystal layer in the liquid crystal display device, when d/p=0.48.

[0044]FIG. 30 is a view schematically showing an alignment state ofliquid crystal molecules in the vicinity of the surface of the pictureelement electrode in the liquid crystal display device, when d/p=0.48.

[0045]FIG. 31 is a diagram showing a transmission intensity distributionin the liquid crystal display device, when d/p=0.48.

[0046]FIG. 32 is a view schematically showing a relationship betweendifferent portions of a picture element region and how liquid crystalmolecules are aligned in these portions in the liquid crystal displaydevice.

[0047]FIG. 33 is a view schematically showing an alignment state ofliquid crystal molecules when vertical alignment films on the respectivesubstrate surfaces are assumed to have no alignment regulating forces onthe liquid crystal molecules.

[0048]FIG. 34 is a view schematically showing an alignment state ofliquid crystal molecules when the vertical alignment films on therespective substrate surfaces are assumed to have alignment regulatingforces so that some of the liquid crystal molecules maintain thevertically aligned state even under applied voltage.

[0049]FIG. 35 is a view schematically showing a twisted structure of theliquid crystal layer when the alignment regulating forces are assumed tobe absent.

[0050]FIG. 36 is a view schematically showing a twisted structure of theliquid crystal layer when the alignment regulating forces are assumed tobe present so that some of the liquid crystal molecules maintain thevertically aligned state even under applied voltage.

[0051]FIG. 37 is a graph representing a numerical range of d·Δn/λ withrespect to maximum effective voltage, defining a numerical range inwhich brightness can be improved.

[0052]FIG. 38 is a graph showing a numerical range of d/p with respectto maximum effective voltage, defining a numerical range in whichbrightness can be improved.

[0053]FIG. 39 is a top view showing an alternative form of the pictureelement electrode in accordance with a modification example of theliquid crystal display device.

[0054]FIG. 40 is a top view showing another alternative form of thepicture element electrode in accordance with another modificationexample of the liquid crystal display device.

[0055]FIG. 41 is a top view showing yet another alternative form of thepicture element electrode in accordance with yet another modificationexample of the liquid crystal display device.

[0056]FIG. 42 is a top view showing still another alternative form ofthe picture element electrode in accordance with still anothermodification example of the liquid crystal display device.

[0057]FIG. 43 is a top view showing yet another alternative form of thepicture element electrode in accordance with yet another modificationexample of the liquid crystal display device.

[0058]FIG. 44 is a top view showing still another alternative form ofthe picture element electrode in accordance with still anothermodification example of the liquid crystal display device.

[0059]FIG. 45 is a top view showing yet another alternative form of thepicture element electrode in accordance with yet another modificationexample of the liquid crystal display device.

[0060]FIG. 46 is a top view showing still another alternative form ofthe picture element electrode in accordance with still anothermodification example of the liquid crystal display device.

[0061]FIG. 47 is a top view showing yet another alternative form of thepicture element electrode in accordance with yet another modificationexample of the liquid crystal display device.

[0062]FIG. 48 is a top view showing a unit lattice in which a unit solidsection has a circular shape.

[0063]FIG. 49 is a top view showing a unit lattice in which an openinghas a circular shape.

[0064]FIG. 50 is a graph plotting the area ratio of the solid sectionwith respect to the pitch of the picture element region for the unitlattice with the circular unit solid section and for the unit latticewith the circular opening.

DESCRIPTION OF THE EMBODIMENTS

[0065] The following will explain an embodiment of the present inventionwith reference to FIGS. 1 through 50. A liquid crystal display device inaccordance with the present embodiment does not generate a quenchingpattern in spite of its high area-transmission-intensity, and therebyproduces high quality display. As shown in FIG. 2, the liquid crystaldisplay device is provided with a liquid crystal cell 100 of a verticalalignment mode, and polarization plates 101 and 102 that arerespectively disposed on both sides of the liquid crystal cell 100.

[0066] The liquid crystal cell 100 includes an active matrix substrate100 a such as a thin film transistor (TFT) substrate (hereinafterreferred to as “thin film transistor (TFT) substrate”), a countersubstrate 100 b such as a color filter substrate (hereinafter alsoreferred to as “color filter substrate”), and a liquid crystal layer 30interposed between the TFT substrate 100 a and the counter substrate 100b. Note that, the TFT substrate 100 a and the counter substrate 100 bcorrespond to first and second substrates, respectively, as recited inthe claims.

[0067] The liquid crystal layer 30 is made of a material prepared byadding a chiral dopant to a nematic liquid crystal material having anegative dielectric anisotropy. Further, the amount of chiral dopantadded is set so that d/p of the liquid crystal layer 30 falls within anumerical range to be described later, and that d·Δn/λ of the liquidcrystal layer 30 falls within a numerical range to be described later.

[0068] Vertical alignment films 13 and 23 are respectively provided onthe surfaces of the TFT substrate 100 a and the counter substrate 100 bfacing the liquid crystal layer 30. With the vertical alignment films 13and 23, liquid crystal molecules 30 a in the liquid crystal layer 30 arevertically aligned with respect to the surfaces of the verticalalignment films 13 and 23 when no voltage is applied to the liquidcrystal layer 30, as in the state shown in FIG. 2. Here, the liquidcrystal layer 30 is in a vertically aligned state.

[0069] Note that, depending on the type of the vertical alignment films13 and 23 and the type of the liquid crystal material, the liquidcrystal molecules 30 a in the liquid crystal layer 30 in the verticallyaligned state may be slightly tilted with respect to normal to thesurfaces of the vertical alignment films 13 and 23 (substrate surfaces).In general, however, the term “vertically aligned state” is referred towhenever the liquid crystal molecules 30 a are aligned substantiallyvertically to the surfaces of the vertical alignment films 13 and 23;namely, a state where a liquid crystal molecular axis (also called as“axial direction”) of the liquid crystal molecules 30 a is aligned at anangle of approximately 85 degrees through 90 degrees with respect to thesurfaces of the vertical alignment films 13 and 23.

[0070] The TFT substrate 100 a of the liquid crystal cell 100 includes atransparent substrate (glass substrate, for example) 11, a pictureelement electrode (first electrode) 12 formed on a surface of thetransparent substrate 11, and the vertical alignment film 13 formed onthe surface of the TFT substrate 100 a facing the liquid crystal layer30. On the other hand, the counter substrate 100 b includes atransparent substrate (glass substrate, for example) 21, a counterelectrode (second electrode) 22 formed on a surface of the countersubstrate 11, and the vertical alignment film 23 formed on the surfaceof the counter substrate 100 b facing the liquid crystal layer 30. Thealigned state of the liquid crystal layer 30 in each picture elementchanges in response to the voltage applied to the picture elementelectrode 12 and the counter electrode 22 facing each other via theliquid crystal layer 30 in between. Display is carried out by utilizingthe phenomenon in which the polarizing state and the quantity of lightthat passes through the liquid crystal layer 30 change in accordancewith a change in aligned state of the liquid crystal layer 30.

[0071] Note that, as used herein, a portion of the liquid crystaldisplay device that corresponds to a “picture element,” which is theminimum unit of display, is hereinafter referred to as a “pictureelement region.” In a color liquid crystal display device, “pictureelements” of R, G, and B correspond to one “pixel.” In an active matrixliquid crystal display device, the picture element region is defined bythe picture element electrode and the counter electrode opposite thepicture element electrode. Further, in a simple matrix liquid crystaldisplay device to be described later, the picture element region isdefined by a region where stripe column electrodes cross stripe rowelectrodes orthogonal to each other. Note that, in the strict sense, inan arrangement where a black matrix is provided, an area correspondingto an opening of the black matrix corresponds to the picture elementregion, among the area to which a voltage is applied in accordance witha state to be displayed.

[0072] As a preferred example of the liquid crystal cell 100, thefollowing will explain in detail a case where a plurality of separatedelectrodes (sub pixels) are formed in one picture element region on theside of one of the substrates (100 a), whereby a closed region is formedwith respect to an electric field, and the alignment is controlled usingan inclined electric field generated from the edges of the electrodes.

[0073] Specifically, the picture element electrode 12 is made from aconductive film (ITO film, for example). As shown in FIG. 3, a pluralityof openings are formed in the picture element electrode 12, for example,by removing the conductive film. Note that, FIG. 3 is a plan view (topview) of the liquid crystal cell 100 of the liquid crystal displaydevice viewed from a direction normal to the substrate. FIG. 2 is across-sectional view taken along line 1B-1B′ of FIG. 3. Hereinafter, aportion where the conductive film remains (portion except the openings12 a) is referred to as a solid section 12 b. The openings 12 a areformed in each picture element electrode 12, whereas the solid section12 b is basically a single continuous sheet of conductive film.

[0074] In the present embodiment, the openings 12 a are arranged so thatthe centers of the respective openings 12 a form a square lattice, andfour of the openings 12 a whose centers are positioned on four latticepoints that form a unit lattice substantially surround the solid section(hereinafter referred to as “unit solid section”) 12 c, which issubstantially circular in shape. Each opening 12 a has four sides(edges) each having a quadrant arc shape, and is formed into asubstantially star shape having a four-fold axis of symmetry at itscenter.

[0075] Note that, in order to obtain stable alignment over the entirearea of the picture element region A, the unit lattice is preferablyformed so that it occupies edge portions of the picture elementelectrode 12 as well. Thus, as shown in FIG. 3, the edge portions of thepicture element electrode 12 is preferably patterned into a shapecorresponding to approximately a half of the opening 12 a (at the sidesof the picture element electrode 12 ) and approximately a quarter of theopening 12 a (at the corners the picture element electrode 12 ). On theother hand, the openings 12 a positioned at the central portion of thepicture element electrode 12 (four openings 12 a whose centers arepositioned on four lattice points that form a unit lattice so as tosurround the unit solid section 12 c) have substantially the same shapeand the same size. The unit solid sections 12 c each positioned in theunit lattice formed with the opening 12 a are substantially circular inshape and have substantially the same shape and the same size. Adjacentones of the unit solid sections 12 c are connected with one another, soas to make up the solid section 12 b which substantially serves as asingle conductive film.

[0076] When a voltage is applied across the counter electrode 22 and thepicture element electrode 12 as arranged above, the edge portions of theopenings 12 a generate an inclined electric field so as to form aplurality of liquid crystal domains each having a radially inclinedalignment. The liquid crystal domain is formed for a regioncorresponding to each opening 12 a and for a region corresponding toeach unit solid section 12 c.

[0077] In the liquid crystal cell 100 as arranged above, when thepicture element electrode 12 and the counter electrode 22 have the samepotential (when no voltage is applied to the liquid crystal layer 30 ),the liquid crystal molecules 30 a within the picture element region arealigned vertically to the surfaces of both the substrates 100 a and 100b, as shown in FIG. 2.

[0078] On the other hand, when a voltage is applied to the liquidcrystal layer 30, a potential gradient, which is represented byequipotential lines EQ (orthogonal to the electric field line), isformed in the liquid crystal layer 30, as shown in FIG. 4. Theequipotential lines EQ in the liquid crystal layer 30 are parallel tothe surfaces of the solid section 12 b and the counter electrode 22 inan area between the solid section 12 b of the picture element electrode12 and the counter electrode 22. On the other hand, in an areacorresponding to the opening 12 c of the picture element electrode 12,the equipotential lines EQ drop towards the opening 12 a in the liquidcrystal layer 30. That is, an inclined electric field is formed in theliquid crystal layer 30 on an edge portion (peripheral portion of theopening 12 a and boundary portion between the opening 12 a and the solidsection 12 b) EG of the opening 12 a, as represented by the inclinedequipotential lines EQ in FIG. 4.

[0079] Here, the liquid crystal molecules 30 a having a negativedielectric anisotropy are acted upon by a torque that causes the axialdirection of the liquid crystal molecules 30 a to align itself parallelto the equipotential lines EQ (perpendicular to the electric fieldline). Accordingly, the liquid crystal molecules 30 a on the edgeportion EG are tilted (rotated) in a clockwise direction on the rightside of the edge portion EG and in a counterclockwise direction on theleft side of the edge portion EG, as indicated by the arrows in FIG. 4.As a result, the liquid crystal molecules 30 a in the liquid crystallayer 30 are aligned parallel to the equipotential lines EQ, except atthe central portion of the unit solid section 12 c and the centralportion of the opening 12 a, as shown in FIG. 5. Note that, FIG. 4schematically shows a state where the alignment of the liquid crystalmolecules 30 a has started to change in accordance with an appliedvoltage to the liquid crystal layer 30 (ON initial state), whereas FIG.5 schematically shows a state where the aligned state of the liquidcrystal molecules 30 a in response to the applied voltage has reached asteady state.

[0080] More specifically, as shown in FIG. 6, when an electric field asrepresented by the equipotential line EQ perpendicular to the axialdirection of the liquid crystal molecule 30 a generates, the liquidcrystal molecule 30 a is acted upon by a torque to tilt clockwise orcounterclockwise with equal probability in either direction. Thus, theliquid crystal layer 30, which is interposed between the electrodes ofthe parallel-plate structure facing each other, contains liquid crystalmolecules 30 a that are acted upon by a clockwise torque and liquidcrystal molecules 30 a that are acted upon by a counterclockwise torque.This may prevent the liquid crystal layer 30 from smoothly aligningitself to an aligned state in accordance with an applied voltage.

[0081] In the present embodiment, however, an inclined electric field isformed on the edge portion EG. With the electric field as represented bythe equipotential line EQ which is inclined with respect to the axialdirection of the liquid crystal molecule 30 a (inclined electric field),the liquid crystal molecules 30 a tilt in a direction (counterclockwisein FIG. 7) that requires less tilting to be parallel to theequipotential line EQ, as shown in FIG. 7.

[0082] On the other hand, the liquid crystal molecule 30 a positioned ata portion where an electric field as represented by the equipotentialline EQ perpendicular to the axial direction of the liquid crystalmolecule 30 a tilts in the same direction as the liquid crystal molecule30 a that is positioned on the inclined equipotential line EQ, so as tohave a continuous (uniform) alignment with this liquid crystal molecule30 a, as shown in FIG. 8. Thus, as shown in FIG. 9, when an electricfield is applied whose equipotential lines EQ form continuousirregularities, the liquid crystal molecule 30 a that is positioned on aflat portion of the equipotential line EQ aligns in such a directionthat the direction of alignment conforms to the alignment directionregulated by the liquid crystal molecule 30 a that is positioned on aportion of the equipotential line EQ that is continuous from thecontinuous portion and that is inclined with respect to the liquidcrystal molecules 30 a. Note that, as used herein, “positioned on anequipotential line EQ” means “positioned within an electric fieldrepresented by equipotential lines EQ.” Thus, stabilization of thealignment direction starts from the liquid crystal molecule 30 apositioned on the inclined portion of the equipotential line EQ, andproceeds through the liquid crystal molecules 30 a at the centralportion of the solid section and toward the liquid crystal molecules 30a at the central position of the opening 12 a.

[0083] In the region above the opening 12 a, the liquid crystalmolecules 30 a positioned in the vicinity of the center of the opening12 a are influenced, to substantially the same extent, by the alignmentsof the liquid crystal molecules 30 a on the opposite edge portions EGacross the opening 12 a. Thus, as shown in FIG. 5, the liquid crystalmolecules 30 a at the central portion of the opening 12 a maintains itsvertically aligned state with respect to the equipotential line EQ. Onthe other hand, the liquid crystal molecules 30 a that are off thecenter of the opening 12 a are tilted under the influence of thealignments of the liquid crystal molecules 30 a on the edge portions EGof the respective sides, so as to form an inclined alignment that issymmetrical with respect to the center SA of the opening 12 a.

[0084] Likewise, in a region above the unit solid section 12 csubstantially surrounded with the openings 12 a, the liquid crystalmolecules 30 a in the corresponding region of the unit solid section 12c are influenced by the alignments of the liquid crystal molecules 30 aon the edge portions EG of the opening 12 a. Further, the liquid crystalmolecules 30 a positioned in the vicinity of the center of the unitsolid section 12 c are influenced, to substantially the same extent, bythe alignments of the liquid crystal molecules 30 a on the opposite edgeportions EG across the unit solid section 12 c. As a result, the liquidcrystal molecules 30 a on the unit solid section 12 c form an inclinedalignment that is symmetrical with respect to the center SB of the unitsolid section 12 c (corresponding to the center of the unit latticeformed by the openings 12 a).

[0085] Therefore, as described above, a change in aligned state is setoff by the liquid crystal molecules 30 a positioned on the inclinedequipotential lines EQ, and proceeds until the liquid crystal molecules30 a within the picture element region reach a steady state. Thealignments of the liquid crystal molecules 30 in a steady state areschematically shown in FIG. 5 by the cross section of the liquid crystallayer.

[0086] Meanwhile, the aligned state of the liquid crystal layer 30 in anin-plane direction of the substrate changes in response to an appliedvoltage in the manner shown in FIGS. 10 through 12. Namely, under noapplied voltage to the liquid crystal layer 30, the aligned direction ofthe liquid crystal molecules 30 a in the picture element region areregulated by the vertical alignment films 13 and 23, so that the liquidcrystal molecules 30 are in a vertically aligned state, as shown in FIG.10. Note that, in the drawings showing the aligned state of the liquidcrystal molecules 30 a as viewed from a direction normal to thesubstrate, the black end of an ellipsoid representing the liquid crystalmolecule 30 a indicates that the liquid crystal molecule 30 a is tiltedso that the substrate on which the picture element electrode 12 havingthe openings 12 a is provided is closer to the black end than the otherend.

[0087] When an electric field represented by the equipotential lines EQshown in FIG. 4 is generated by the electric field applied across theliquid crystal layer 30, the liquid crystal molecules 30 a having anegative dielectric anisotropy are acted upon by a torque that causesthe axial directions of the liquid crystal molecules to be parallel tothe equipotential lines EQ. As described above, the alignments of theliquid crystal molecules 30 a under the electric field represented bythe equipotential lines EQ perpendicular to the molecular axis of theliquid crystal molecules 30 a are not easily changed (tilted orrotated), because the direction of tilting (rotation) of the liquidcrystal molecules 30 a is not uniquely defined. On the other hand, thealignments of the liquid crystal molecules 30 a under the equipotentiallines EQ that are inclined with respect to the molecular axis of theliquid crystal molecules 30 a are easily changed, because the tilting(rotation) direction is uniquely defined. Thus, as shown in FIG. 11, theliquid crystal molecules 30 a start tilting from a portion where themolecular axis of the liquid crystal molecules 30 a is tilted withrespect to the equipotential lines EQ, namely the edge portions EG ofthe opening 12 a. Then, the surrounding liquid crystal molecules 30 aare tilted so as to conform to the alignments of the tilted liquidcrystal molecules 30 a on the edge portions EG of the opening 12 a. As aresult, the axial directions of the liquid crystal molecules 30 astabilize in the state shown in FIG. 12. Note that, in the presentembodiment, the alignment involves twist because the liquid crystalmolecules 30 a have a natural twist pitch p. The influence of the twistwill be discussed later.

[0088] Here, the opening 12 a in accordance with the present embodimenthas a rotationally symmetrical shape. Thus, the liquid crystal molecules30 a within a picture element region start tilting from the edgeportions EG of the opening 12 a toward the center of the opening 12 awhen a voltage is applied. Further, under applied voltage, thealignment-regulating forces exerted on the liquid crystal molecules 30 aby the edge portions EG are balanced out in the vicinity of the centerSA of the opening 12 a. Thus, while the liquid crystal molecules 30 a inthe vicinity of the center SA of the opening 12 a retain its verticallyaligned state with respect to the substrate surface, the surroundingliquid crystal molecules 30 a are aligned in a radially inclined manneraround the liquid crystal molecules 30 a in the vicinity of the centerSA of the opening 12 a. The aligned state of these surrounding liquidcrystal molecules 30 a shows a continuous (smooth) change.

[0089] As a result, when viewed from a direction vertical to the displaysurface of the liquid crystal cell 100 (vertical to the surfaces of thesubstrates 100 a and 100 b), the axial directions of the liquid crystalmolecules 30 a are radially aligned with respect to the center of theopening 12 a. Note that, in the present specification, a state where theliquid crystal molecules 30 a of the liquid crystal layer 30 are alignedin a radially inclined manner is referred to as a “radially inclinedalignment.” Further, a portion of the liquid crystal layer having aradially inclined alignment around any given center is referred to as aliquid crystal domain.

[0090] Likewise, in a portion corresponding to the unit solid section 12c, the liquid crystal molecules 30 a also have a radially inclinedalignment, forming a liquid crystal domain in which the liquid crystalmolecules 30 a have a radially inclined alignment. More specifically,the liquid crystal molecules 30 a are tilted so as to conform to thealignments of the liquid crystal molecules 30 a that are tilted by theinclined electric field generated at the edge portions EG of the opening12 a. Under applied voltage, the alignment regulating forces exerted onthe liquid crystal molecules 30 a by the edge portions EG balance out inthe vicinity of the center SB of the unit solid section 12 c.Consequently, when a voltage is applied, the liquid crystal molecules 30a in the vicinity of the center SB of the unit solid section 12 c retainits vertically aligned state with respect to the substrate surface;while the surrounding liquid crystal molecules 30 a are aligned in sucha manner that the in-plane component of the alignment directions isradially aligned around the liquid crystal molecules 30 a in thevicinity the center SB of the unit solid section 12 c so that componentof the normal direction is inclined. In this state, the aligned state ofthe surrounding liquid crystal molecules 30 a shows a continuous(smooth) change.

[0091] As described above, the picture element electrode 12 of theliquid crystal display device in accordance with the present embodimenthas a plurality of openings 12 a. In response to an applied voltage, thepicture element electrode 12 generates such an electric field in thepicture element region in the liquid crystal layer 30 that the electricfield is represented by equipotential lines EQ having an inclinedportion. The liquid crystal molecules 30 a having a negative dielectricanisotropy within the liquid crystal layer 30 are in a verticallyaligned state under no applied voltage. When a voltage is applied to thepicture element electrode 12, a change in alignment of the liquidcrystal molecules positioned on the inclined equipotential lines EQtriggers a change in alignment direction of the liquid crystal molecules30 a, thereby forming the liquid crystal domain of a stable radiallyinclined alignment for the opening 12 a and for the solid section 12 b.Here, in response to an applied voltage to the liquid crystal layer 30,the alignments of the liquid crystal molecules in the liquid crystaldomain changes. This enables the liquid crystal display device to changeits display state in accordance with the applied voltage.

[0092] The radially inclined alignment in the liquid crystal domainformed on the unit solid section 12 c and the radially inclinedalignment in the liquid crystal domain formed on the opening 12 a arecontinuous, and the radially inclined alignment in either liquid crystaldomain conforms to the alignments of the liquid crystal molecules 30 aon the edge portions EG of the opening 12 a. Accordingly, the liquidcrystal molecules 30 a in the liquid crystal domain formed on theopening 12 a are aligned in the form of a cone opening upward (open tothe substrate 100 b), while the liquid crystal molecules 30 a formed onthe unit solid section 12 c are aligned in the form of a cone openingdownward (open to the substrate 100 a). Thus, the radially inclinedalignment in the liquid crystal domain formed on the opening 12 a andthe radially inclined alignment in the liquid crystal domain formed onthe unit solid section 12 c are continuous to each other. Thiseliminates a disclination line (alignment defect) along the boundary ofthe liquid crystal domains, thereby preventing impairment of displayquality caused by the disclination line.

[0093] Note that, with the described arrangement of the presentembodiment in which the liquid crystal domains each having a radiallyinclined alignment of the liquid crystal molecules 30 a are arranged inthe form of a square lattice over the entire picture element region, theprobability of existence of the liquid crystal molecules 30 a aligned inthe respective axial directions assumes rotational symmetry, therebyrealizing high quality display without unevenness in every viewing angledirection. Here, to reduce the viewing angle dependency of the liquidcrystal domain having a radially inclined alignment, the liquid crystaldomain preferably has a high-fold axis of symmetry (preferably two orgreater fold axis of symmetry, and more preferably four-fold axis ofsymmetry). Further, to reduce the viewing angle dependency over theentire picture element region, a plurality of liquid crystal domainsformed in the picture element region preferably form an array (squarelattice, for example) represented by a combination of units (unitlattice, for example) with a high-fold axis of symmetry (preferably, atwo or greater fold axis of symmetry, and more preferably a four orgreater fold axis of symmetry).

[0094] In the liquid crystal display device using the liquid crystalcell 100, almost all of the liquid crystal molecules 30 a in the liquidcrystal layer 30 are in the vertically aligned state under no appliedvoltage. Thus, in the arrangement where the liquid crystal cell 100 issandwiched between the polarization plates 101 and 102 as shown in FIG.2, the incident light enters the liquid crystal cell 100 as linearlypolarized light through the polarization plate 101. Since thebirefringent effect does not occur in the liquid crystal cell 100, theincident light passes through the liquid crystal cell 100 whilesubstantially maintaining the state of polarization, and reaches thepolarization plate 102. Here, the polarization axis of the polarizationplate 101 and the polarization axis of the polarization plate 102 arearranged to cross each other at a right angle. Thus, most of the lightthat passes through the liquid crystal cell 100 is absorbed in thepolarization plate 102. As a result, the liquid crystal display devicehas black display under no applied voltage. Particularly, in the liquidcrystal display device of the present embodiment, the liquid crystalmolecules 30 a in the liquid crystal cell 100 can achieve asubstantially complete vertically aligned state for black display. Thisprevents light leaking almost completely, thereby realizing highcontrast display.

[0095] On the other hand, under applied voltage, the liquid crystalmolecules 30 a of the liquid crystal layer 30 are in a radially-inclinedalignment state. Thus, in the arrangement where the liquid crystal cell100 is sandwiched between the polarization plates 101 and 102, theincident light enters the liquid crystal cell 100 as linearly polarizedlight through the polarization plate 101. Since the birefringent effectoccurs in the liquid crystal cell 100, the incident light passes throughthe liquid crystal cell 100 by changing the state of polarization, andreaches the polarization plate 102. Here, the component of the lightthat has changed its state of polarization to coincide with thedirection of the polarization axis of the polarization plate 102 passesthrough the polarization plate 102 and leaves the polarization plate 102to realize white display. Further, a change in applied voltage bringsabout a change in inclination amount for the radially inclined alignmentand a corresponding change in the amount of birefringent effectgenerated by the inclination. As a result, the quantity of light thatemerges from the polarization plate 102 is varied. This realizesgradation display in accordance with the applied voltage.

[0096] Further, because of the radially inclined alignment, theprobability of existence of the liquid crystal molecules 30 a aligned inthe respective axial directions assumes rotational symmetry, so that theregions where the liquid crystal molecules 30 a are aligned in differentdirections optically compensate with one another. As a result, no matterwhich direction a user views the liquid crystal display device, theintensity of emergent light (brightness of picture elements) issubstantially the same over the entire picture element region, therebyachieving a large viewing angle.

[0097] In the event where the liquid crystal layer does not have atwisted structure, sandwiching the liquid crystal cell 100 between thetwo polarization plates 101 and 102 whose polarization axes are crossedin a crossed nicole arrangement causes a phenomenon known as a quenchingpattern. More specifically, when the liquid crystal molecules 30 a arealigned in different directions in the liquid crystal cell 100 as in theradially inclined alignment, the directions of the polarization axes ofthe polarization plates are related to the respective alignmentdirections of the liquid crystal molecules 30 a under applied voltage insuch a manner that the birefringence effect, which is generated in eachminute unit region according to the relationship between thepolarization directions and the alignment directions, is generated to adifferent extent in each minute unit region. The differences inbirefringence effect between minute unit regions are recognized asdifferences in luminance (quenching pattern). That is, the phenomenonreduces the number of minute unit regions that can effectively transmitlight, thereby decreasing luminance. Note that, the minute unit regionrefers to a region in which the liquid crystal layer is divided on themolecular level of the liquid crystal parallel to the layer direction ofthe liquid crystal layer. Specifically, the minute unit region is acolumn of liquid crystal molecules in the thickness direction of theliquid crystal layer, as shown in FIGS. 33 through 36 to be describedlater.

[0098] In contrast, in the liquid crystal display device in accordancewith the present embodiment, d/p of the liquid crystal cell 100 is setin accordance with a maximum applied effective voltage (appliedeffective voltage for white display) Vmax [V], as given by the followinginequity (1).

d/p(min)≦d/p≦d/p(max),

where d/p(max)=0.0021×(Vmax)²−0.0458×(Vmax)+0.65, and

d/p(min)=0.0021×(Vmax)²−0.0458×(Vmax)+0.50   (1).

[0099] Note that, d [μm] is the gap of the liquid crystal cell 100, andp [μm] is the natural twist pitch of the liquid crystal (twist amountfor unregulated liquid crystal; the length required for twisting theliquid crystal 360 degrees). Here, in the liquid crystal cell 100 inaccordance with the present embodiment, p is set by adding a chiraldopant to the liquid crystal.

[0100] Further, in the present embodiment, d·Δn/λ of the liquid crystalcell 100 is set in accordance with a maximum applied effective voltage(applied effective voltage for white display) Vmax [V], as given by thefollowing inequity (2).

d·Δn/λ(min)≦d·Δn/λ≦d·Δn/λ(max),

where d·Δn/λ(max)=−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.124,and

d·Δn/λ(min)=−0.00026×(Vmax)³+0.016—(Vmax)²−0.2281×(Vmax)+1.7603   (2).

[0101] Note that, An is the birefringence anisotropy, and λ [μm] is thewavelength of transmitted light. FIG. 1 shows graphs representing anumerical range for d/p with respect to different values of maximumapplied effective voltage and a numerical range for d·Δn/λ with respectto different values of maximum applied effective voltage. Namely, asshown in FIG. 1, d/p and d·Δn/λ are set to satisfy the inequities (1)and (2), respectively, in accordance with the maximum applied effectivevoltage Vmax.

[0102] As a result, in the liquid crystal display device in accordancewith the present embodiment, the quenching pattern is invisible, andeach minute unit region has the maximum transmission intensity, therebysurely obtaining a liquid crystal display device having remarkablyimproved display quality.

[0103] The inequities (1) and (2) were derived in the following manner.Specifically, by means of simulation and using the liquid crystaldisplay device as arranged above, d·Δn/λ that maximizes the areatransmission intensity (normalized value of integration result oftransmission intensity in the minute unit regions within the plane, forexample, within one picture element) was calculated for each combinationof the maximum applied effective voltage Vmax and d/p.

[0104] The result of simulation showed that when the maximum appliedeffective voltage is 10 [V] for example, the area transmission intensitywith respect to each value of d/p varies with d·Δn/λ in the manner shownin FIG. 13. In this case, when d/p=0.38 for example, the maximum areatransmission intensity is obtained with d·Δn/λ=1.03. When the maximumapplied effective voltage is 6 [V] for example, the area transmissionintensity with respect to each value of d/p varies with d·Δn/λ in themanner shown in FIG. 14. In this case, when d/p=0.38 for example, themaximum area transmission intensity is obtained with d·Δn/λ=1.10.Further, when the maximum applied effective voltage is 4 [V] forexample, the area transmission intensity with respect to each value ofd/p varies with d·Δn/λ in the manner shown in FIG. 15. In this case,when d/p=0.38 for example, the maximum area transmission intensity isobtained with d·Δn/λ=1.31.

[0105] Furthermore, using the value of d·Δn/λ that maximizes the areatransmission intensity, a transmission intensity distribution in aliquid crystal domain (sub pixel) was calculated by means of simulationto evaluate whether or not a quenching pattern is suppressed to theextent where it cannot be recognized. Note that, in the simulation, theliquid crystal director was calculated by three-dimensional calculationusing director-vector equation of motion based on the Eriksen-Leslietheory, and optical calculation was carried out through analysis usingJones matrix.

[0106] As an example, under the condition where Vmax=6 [V], and forliquid crystal display devices with d/p=0.13, 0.38, and 0.48 and for aliquid crystal display device in which the liquid crystal does not havea twisted structure, FIGS. 16 through 31 show alignment directiondistributions and transmission intensity distributions of the liquidcrystal molecules 30 a, wherein the alignment direction distributionswere measured (i) in the vicinity of the surface of the counterelectrode 22, (ii) in the vicinity of the middle of the liquid crystallayer 30, and (iii) in the vicinity of the surface of the pictureelement electrode 12. Here, d·Δn/λ is set to yield the maximum areatransmission intensity for each value of d/p. It should be noted thatthe above simulation was carried out for combinations of (i) adielectric anisotropy Δε in a range of −2.5 and −6.5 and (ii) an elasticconstant ratio K11/K33 in a range of 0.9 and 2.0. In FIGS. 13 through31, however, only representative drawings with a dielectric anisotropyΔε of −4 and an elastic constant ratio K33/K11 of 1.1 for the liquidcrystal layer 30 are shown as an example among the simulation results.

[0107] When the liquid crystal does not have a twisted structure, thealignment directions of the liquid crystal molecules were substantiallythe same (i) in the vicinity of the surface of the counter electrode 22,(ii) in the vicinity of the middle of the liquid crystal layer 30(thicknesswise), and (iii) in the vicinity of the surface of the pictureelement electrode 12, as shown in FIGS. 16 through 18. Accordingly, in aliquid crystal region where the liquid crystal molecules 30 a arealigned in a direction different from the directions of the polarizationaxes of the polarization plates 101 and 102, birefringent effect isgenerated and the light passes therethrough. In contrast, in a regionwhere the liquid crystal molecules 30 a are aligned in the samedirection as the direction of the polarization axes, birefringenceeffect does not generate but a clear cross-shaped quenching pattern isgenerated as shown in FIG. 19.

[0108] When d/p=0.13, the alignment directions of the liquid crystalmolecules 30 a were slightly different from one another (i) in thevicinity of the surface of the counter electrode 22, (ii) in thevicinity of the middle of the liquid crystal layer 30, and (iii) in thevicinity of the surface of the picture element electrode 12, and theliquid crystal layer 30 had a twisted structure between the twosubstrates, as shown in FIGS. 20 through 23. Further, a swirlingalignment was generated in an in-plane direction around the centralportion of the domain (the unit solid section 12 c in the drawings).Accordingly, a quenching pattern having a swirling shape appeared in thetransmission intensity distribution as shown in FIG. 23. However, thequenching pattern is fainter and the area transmission intensity ishigher compared with the arrangement where the liquid crystal does nothave a twisted structure, because the liquid crystal layer 30 in thiscase generates an optical rotatory effect by its twisted structure.

[0109] When d/p=0.38, the alignment directions of the liquid crystalmolecules 30 a (i) in the vicinity of the surface of the counterelectrode 22, (ii) in the vicinity of the middle of the liquid crystallayer 30, and (iii) in the vicinity of the surface of the pictureelement electrode 12 differed from one another more significantlycompared with the case where d/p=0.13, so that the twisted structure wasmore remarkable, as shown in FIGS. 24 through 26. Further, in this case,the area transmission intensity was maximum and the quenching patterndisappeared substantially completely, as shown in FIG. 27. In otherwords, while obtaining the maximum transmission intensity for eachminute unit region, the same amount of the birefringent effect oroptical rotatory effect is generated in each minute unit region in thedomain.

[0110] Further, when d/p=0.48 by increasing the twist amount of theliquid crystal, the alignment directions of the liquid crystal molecules30 a (i) in the vicinity of the surface of the counter electrode 22,(ii) in the vicinity of the middle of the liquid crystal layer 30, and(iii) in the vicinity of the surface of the picture element electrode 12differed from one another even more widely, as shown in FIGS. 27 through30. However, in this case, a quenching pattern appeared even with themaximum area transmission intensity, as shown in FIG. 31. That is, theminute unit regions in the domain had different amounts of birefringenteffect or optical rotatory effect.

[0111] In the manner described above, the transmission intensitydistribution for d·Δn/λ that maximizes the area transmission intensitywere calculated by simulation for each combination of maximum appliedeffective voltage Vmax and d/p, so as to check for the presence orabsence of a quenching pattern. Further, such combinations of d/p,d·Δn/λ, and maximum applied effective voltage Vmax that suppress thequenching pattern to the extent where it cannot be recognized and thatyield high area transmission intensities were extracted from theevaluated combinations, i.e., from the combinations of d/p, d·Δn/λ, andmaximum applied effective voltage Vmax for the liquid crystal cell 100.Then, a range of the combinations so extracted was approximated with aquadratic expression and a cubic expression regarding Vmax, so as toderive the inequities (1) and (2).

[0112] The simulation results confirmed that the quenching pattern isalmost unrecognizable and each minute unit region has a hightransmission intensity when d/p and d·Δn/λ are set to satisfy theinequities (1) and (2). It was also confirmed that when, on the otherhand, d/p and d·Δn/λ do not satisfy the inequities (1) and (2), thequenching pattern appears, and, even when the quenching pattern isabsent, each minute unit region has a low transmission intensity, andconsequently the area transmission intensity is low.

[0113] Here, in order to eliminate the quenching pattern which isgenerated when the liquid crystal cell 100 is sandwiched between the twopolarization plates 101 and 102 whose polarization axes are crosses in across nicole arrangement, it is preferable that the same amount ofbirefringent effect or optical rotatory effect is generated in eachminute unit region, so that the each region has the same transmissionintensity. In the present embodiment, because of the radially inclinedalignment, the angle formed by the polarization direction of lightentering the liquid crystal cell 100 and the alignment direction of theliquid crystal molecules 30 a on the substrate surface on the lightincident side is not uniform for all minute unit regions. Thus, when theliquid crystal layer 30 does not have a twisted structure, i.e., whenonly the birefringent effect is generated, the amount of birefringenteffect generated becomes different from one minute unit region toanother, with the result that the quenching pattern is generated.

[0114] However, when the liquid crystal layer 30 has a twisted structurewith a twist angle of 90 degrees, the same amount of birefringent effector optical rotatory effect is generated in each minute unit region,irrespective of the angle formed by the polarization direction of lightentering the liquid crystal cell 100 and the alignment direction of theliquid crystal molecules 30 a in each minute unit region on thesubstrate surface on the light incident side. That is, it is preferablein the present embodiment that the liquid crystal layer 30 of the liquidcrystal cell 100 is uniformly twisted 90 degrees in all minute unitregions.

[0115] In the present embodiment, the liquid crystal molecules 30 a aretilted in response to an applied voltage so that the axial directions ofthe liquid crystal molecules 30 a are parallel to the equipotentiallines EQ, as described above. Further, in a portion A1 shown in FIG. 32,namely, in the liquid crystal domain other than the central portion andthe edge portion EG, the equipotential lines EQ are substantiallyparallel to the substrate surface. Thus, the liquid crystal molecules 30a in the liquid crystal layer 30 between the substrates 100 a and 100 bare expected to align themselves so that their long axes directsubstantially parallel to the substrate surface over the entire portiondx that extends in the thickness direction, as shown in FIG. 33.

[0116] However, in order to provide a vertically aligned state for theliquid crystal molecules 30 a under no applied voltage, the surfaces ofthe substrates 100 a and 100 b facing the liquid crystal layer 30 areprovided with the vertical alignment films 13 and 23, respectively.Accordingly, due to the alignment regulating forces of the verticalalignment films 13 and 23, the liquid crystal molecules 30 a at portionsdz in the vicinity of the respective substrates retain the verticalalignment state even under applied voltage, as shown in FIG. 34.

[0117] Therefore, as shown in FIG. 34, the liquid crystal molecules 30 athat can attain the birefringent effect by being tilted in response toan applied voltage do not exist over the entire portion dx that extendsin the thickness direction, but exist in a portion dy excluding portionsdz in the vicinity of the substrates. Note that, the thicknesswiselengths of the portions dx, dy, and dz are related to one another bydx=dy+2dz.

[0118] The foregoing explained the case where the liquid crystal layer30 does not have a twisted structure and generates only the birefringenteffect, but the same applies to the case where the liquid crystal layer30 has a twisted structure and generates the optical rotatory effect aswell. Namely, in the liquid crystal cell 100 in accordance with thepresent embodiment, the natural twist pitch p of liquid crystal is setby adding a chiral dopant. However, the in-plane component of thealignment directions (in-plane directions) of the liquid crystalmolecules 30 a are not regulated. Thus, the liquid crystal molecules 30a are expected to be twisted over the entire portion dx that extends inthe thickness direction of the liquid crystal layer 30.

[0119] However, because the regulating forces for vertical alignment arestrong on the substrate surfaces in the vertically aligned liquidcrystal as described above, the liquid crystal molecules 30 a in theportions dz in the vicinity of the substrate surfaces retain thevertically aligned state even when a voltage is applied, as shown inFIG. 36. Accordingly, the liquid crystal molecules 30 a that cangenerate the birefringent effect or optical rotatory effect by beingtilted in response to an applied voltage do not exist over the entireportion dx that extends in the thickness direction, but exist in portiondy excluding the portions dz in the vicinity of the substrates. Notethat, as with the foregoing, the thicknesswise lengths of the portionsdx, dy, and dz are related to one another by dx=dy +2dz.

[0120] Accordingly, even if such a condition (d/p=0.25) is set that thequenching pattern is eliminated most efficiently in theory (conventionaltechnique) when the liquid crystal layer 30 having a twisted alignmentis sandwiched between the polarization plates 101 and 102 which arearranged in a cross nicole fashion, the condition for actuallyeliminating the quenching pattern would be different from thetheoretical condition because the thickness of the portion dy (effectivecell thickness dy) is smaller than the actual cell thickness dx. Forexample, with Vmax=6 [V], the quenching pattern disappears when d/p is0.38 in the described embodiment, which widely differs from 0.25, asdescribed above.

[0121] A proportion of liquid crystal molecules 30 a that retain thevertically aligned state (the thicknesswise length of the portions dz)increases with decrease in applied voltage, and decreases with increasein applied voltage. Accordingly, the effective cell thickness dy changesin accordance with the applied voltage.

[0122] Therefore, in the present embodiment, such a value is set for d/pthat it is larger than the theoretical value that takes into accounttilting of the liquid crystal molecules 30 a in the liquid crystal layer30 over the entire portion dx under applied voltage, and that the valueof d/p is in accordance with the maximum applied effective voltage Vmax,as shown in the inequities (1) and (2) as described above. In this way,in the portion Al shown in FIG. 32, namely, in the portion where most ofthe liquid crystal molecules 30 a are aligned substantially parallel tothe substrate surfaces, the birefringent effect or optical rotatoryeffect can improve the transmission intensity in each minute unit regionand can suppress the quenching pattern to such a degree as to beinvisible.

[0123] Further, by examining the simulation results, a range thatproduces particularly high brightness was extracted from the range thatsatisfies the inequities (1) and (2). The extracted range was then usedfor comparison to find whether or not any decrease in brightness fromthe extracted range was recognizable for the user, in addition to theevaluation of the foregoing simulation for finding whether or not aquenching pattern is recognizable. As a result, a more preferable rangewas confirmed to be the following range.

[0124] Namely, in the range that satisfies the inequities (1) and (2), arange that satisfies the following inequity (3) is more preferable.

d·Δn/λ(min)≦d·Δn/λ≦d·Δn/λ(max),

where d·Δn/λ(max)=−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.041,and

d·Δn/λ(min)=−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+1.891   (3).

[0125] This range is preferable because any condition within the rangepermits the user to see the display without recognizing a difference inbrightness. That is, d·Δn/λ is preferably set in a range betweend·Δn/λ(max) and d·Δn/λ(min) as shown in FIG. 37.

[0126] Similarly, in the range that satisfies the inequities (1) and(2), a range that satisfies the following inequity (4) is alsopreferable.

d/p(min)≦d/p≦d/p(max),

where d/p(max)=0.0021×(Vmax)²−0.0458×(Vmax)+0.63, and

d/p(min)=0.0021×(Vmax)²−0.0458×(Vmax)+0.53   (4).

[0127] This range is preferable because any condition within the rangepermits the user to see the display without recognizing a difference inbrightness. That is, d·Δn/λ is preferably set in a range betweend·Δn/λ(max) and d·Δn/λ(min) as shown in FIG. 38.

[0128] It was also confirmed that, even when the condition thatsatisfies the inequities (1) and (2) does not satisfy the inequity (3)or (4), the transmission intensity decreases only to the extent that theuser can recognize a difference in brightness , compared with the casewhere at least one of the inequities (3) and (4) is satisfied.

[0129] Incidentally, the foregoing described an example where theopening 12 a has a substantially star shape, the unit solid section 12 chas a substantially circular shape, and they are arranged in the form ofa square lattice, as shown in FIG. 3. However, the shape and thearrangement of the opening 12 a and the unit solid section 12 c are notlimited to the example shown in FIG. 3.

[0130] For example, as shown in FIGS. 39 and 40, the opening 12 a andthe unit solid section 12 c may be slightly distorted form the shapeshown in FIG. 3. In this arrangement, each of the openings 12 a has adistorted star shape, and each of the unit solid sections 12 c has asubstantially ellipsoidal shape (distorted circular shape). Thus, theopening 12 a and the unit solid section 12 c in this arrangement have atwo-fold axis of symmetry (not a four-fold axis of symmetry). Further,the openings 12 a and the unit solid sections 12 c are orderly arrangedso as to form a rectangular unit lattice. Further, in this arrangement,the liquid crystal domain having a radially inclined alignment is alsoformed for the opening 12 a and for the unit solid section 12 c by theinclined electric field generated from the edge portions of the opening12 a. Therefore, it is possible to obtain a liquid crystal displaydevice having high display quality and good viewing anglecharacteristics, as in the case shown in FIG. 3.

[0131] Further, as shown in FIGS. 41 and 42, the openings 12 a may havea substantially cross shape and may be arranged in the form of a squarelattice so that each unit solid section 12 c has a substantially squareshape. Note that, in FIG. 42, the four corners of the unit solid section12 c are linearly cut. Moreover, the openings 12 a and the unit solidsections 12 c may be distorted and arranged to form a rectangular unitlattice. Even with the orderly arrangement of the unit solid sections 12c each having a substantially rectangular shape (including both squareand rectangle), the liquid crystal domain having a radially inclinedalignment can also be formed for the opening 12 a and for the unit solidsection 12 c by the inclined electric field generated from the edgeportions of the opening 12 a. Therefore, it is possible to obtain aliquid crystal display device having high display quality and goodviewing angle characteristics, as in the case shown in FIG. 3.

[0132] It should be noted, however, that, in the arrangements shown inFIGS. 3, 39, and 40, the edges of the opening 12 a are continuous(smooth), and accordingly changes in alignment direction of the liquidcrystal molecules 30 a are also continuous (smooth). Thus, the radiallyinclined alignment can be more stabilized when the opening 12 a and/orthe unit solid section 12 c are circular or ellipsoidal rather thanrectangular.

[0133] From the viewpoint of the continuity of the alignment directionsof the liquid crystal molecules 30 a, the opening 12 a may be defined byfour arcs, as shown in FIG. 43. Further, the opening 12 a may be definedby arc-shaped edges adjacent to the unit solid sections 12 c, as shownin FIG. 44. In either case, the openings 12 a and the unit solidsections 12 c respectively have a four-fold axis of symmetry, and arearranged in the form of a square lattice (having a four-fold axis ofsymmetry). Alternatively, the openings 12 a and the unit solid sections12 c may be deformed into a shape having a two-fold axis of symmetry inthe form of a rectangular lattice (having a two-fold axis of symmetry),in substantially the same manner as in FIGS. 39 and 40. In either case,the edges of the openings 12 a are continuous (smooth), and accordinglychanges in alignment direction of the liquid crystal molecules 30 a arealso continuous (smooth). This enables the liquid crystal molecules tohave a more stable radially inclined alignment, as in the arrangementsof FIGS. 3, 39, and 40.

[0134] In the foregoing examples, the openings 12 a are in the form of asubstantially star shape or a substantially cross shape, and the unitsolid sections 12 c are in the form of a substantially circular shape, asubstantially ellipsoidal shape, a substantially square (rectangular)shape, or a substantially rectangular shape with round corners. Withthese various shapes, the negative/positive pattern for the openings 12a and the unit solid sections 12 c may be reversed. For example, FIG. 45shows a picture element electrode whose positive/positive pattern forthe openings 12 a and the unit solid sections 12 c of the pictureelement electrode 12 shown in FIG. 3 is reversed. The functions of thepicture element electrode remain substantially the same even when itsnegative/positive pattern is reversed. Note that, in some patterns suchas those shown in FIGS. 46 and 47 in which the openings 12 a and theunit solid sections 12 c both have a substantially square shape, thepattern remains the same even when the negative/positive pattern isreversed.

[0135] In the pattern shown in FIG. 45 in which the negative/positivepattern of FIG. 3 is reversed, it is preferable as in FIG. 3, that theedge portions of the picture element electrode 12 partially have theopenings 12 a (approximately a half or quarter of the opening 12 a), soas to form unit solid sections 12 c that are rotationally symmetrical.With this pattern, the edge portions of the picture element region, aswell as the central portion, can obtain the effect of the inclinedelectric field, thereby stably realizing a radially inclined alignmentover the entire picture element region.

[0136] Referring to the picture element electrode 12 of FIG. 3 and thepicture element electrode of FIG. 45 having the reversednegative/positive pattern of FIG. 3, the following describes whichnegative/positive pattern (negative pattern or positive pattern) shouldbe used.

[0137] In either negative/positive pattern, the length of the edges ofthe opening 12 a is the same. Accordingly, the function to generate theinclined electric field is the same in either pattern. However, the arearatio of the unit solid sections 12 c (a proportion of the unit solidsections 12 c in the entire area of the picture element electrode 12)may be different between the negative pattern and positive pattern.Namely, the area of the unit solid sections 12 b (where the conductivefilm actually exists) that generates an electric field to be applied tothe liquid crystal molecules in the liquid crystal layer may bedifferent between these two patterns.

[0138] Here, the voltage applied to the liquid crystal domain formed onthe opening 12 a is lower than the voltage applied to the liquid crystaldomain formed on the solid section 12 b. Accordingly, innormally-black-mode display for example, the liquid crystal domainformed on the opening 12 a becomes dark. Thus, as the area ratio of theopenings 12 a becomes larger, the display brightness tends to decrease.It is therefore preferable that the unit solid sections 12 b have alarger area ratio.

[0139] Whether or not the area ratio of the unit solid sections 12 b isincreased by reversing the negative/positive pattern depends on thepitch (size) of the unit lattice. Namely, the arrangement of FIG. 3 hasa unit lattice pattern as shown in FIG. 48, and the arrangement of FIG.45 has a unit lattice pattern as shown in FIG. 49. Note that, FIG. 49shows the opening 12 a at the center of the drawing. Further, theportions for mutually connecting the unit solid sections 12 c in thearrangement of FIG. 45 (branch portions that extend in four directionsfrom the circular portion) are omitted in FIG. 49.

[0140] It is assumed here that the length (pitch) of a side of thesquare unit lattice is q, and the length of a spacing (side spacing)between the unit lattice and the opening 12 a or the unit solid section12 is s. Then, in order to examine stability or other properties of theradially inclined alignment, a variety of picture element electrodes 12respectively having different pitches p and different side spacings swere formed. As a result, it was found that a side spacing s ofapproximately 2.75 μm or greater is required for the picture elementelectrode 12 having the pattern of FIG. 48 (hereinafter referred to as“positive type pattern”) to generate the required inclined electricfield for obtaining the radially inclined alignment. On the other hand,it was found that a side spacing s of approximately 2.25 μm or less isrequired for the picture electrode 12 having the pattern of FIG. 49(hereinafter referred to as “negative type pattern”) to generate therequired inclined electric field for obtaining the radially inclinedalignment. Table 1 and FIG. 50 show the examination results for the arearatio of the unit solid sections 12 b, when the pitch q was varied withthe side spacings s set to these lower limits. TABLE 1 Area ratio ofsolid section (%) Pitch q Positive Negative [μm] type (a) type (b) 2041.3 52.9 25 47.8 47.2 30 52.4 43.3 35 55.8 40.4 40 58.4 38.2 45 60.536.4 50 62.2 35.0

[0141] As can be seen from Table 1 and FIG. 50, the area ratio of thesolid section 12 b is greater in the positive type (FIG. 48) when thepitch q is not smaller than approximately 25 μm, whereas the area ratioof the solid section 12 b is greater in the negative type (FIG. 49) whenthe pitch q is smaller than approximately 25 μm. Therefore, in respectto the display luminance and stability of alignment, the pattern to beemployed changes according to whether the pitch q of the unit lattice isgreater or smaller than approximately 25 μm. For example, the positivepattern shown in FIG. 48 is preferably employed when three or less unitlattices are provided, whereas the negative pattern shown in FIG. 49 ispreferably employed when four or more unit lattices are provided on thepicture element electrode 12 having a width of 75 μm in the widthdirection. The positive type or negative type should be selected forpatterns other than those as exemplified above, so as to increase thearea ratio of the solid sections 12 b.

[0142] The foregoing described the case where a plurality of square orrectangular unit lattices are formed within a picture element region.However, substantially the same effects can be achieved no matter whatshape the picture element electrode 12 has, provided that the verticallyaligned liquid crystal molecules are aligned.

[0143] To improve the viewing angle dependency of display quality of theliquid crystal display device in all directions, the probability ofexistence of the liquid crystal molecules aligned in all azimuth angledirections preferably assumes rotational symmetry, and more preferablyaxial symmetry, in every picture element region. In other words, theliquid crystal domains formed over the entire picture element region arepreferably arranged to have rotational symmetry and, more preferablyaxial symmetry. However, the liquid crystal domains are not necessarilyrequired to be rotationally symmetrical with respect to the entirepicture element region. Instead, an aggregate of liquid crystal domains(a plurality of liquid crystal domains that are arrayed in the form of asquare lattice for example) which are arrayed to be rotationallysymmetrical (or axially symmetrical) should constitute the pictureelement region in the liquid crystal layer. For example, when theminimum unit of the picture element region is a square lattice (which issymmetrical having a four-fold axis of symmetry), and when the pictureelement region is made up of a combination of the square lattices, theliquid crystal molecules can be aligned with essentially equalprobability for all azimuth angles over the entire picture elementregion. Accordingly, it is not required for the plurality of openings 12a formed in the picture element region to be rotationally symmetricalwith respect to the entire picture element region. Instead, theplurality of openings 12 a should be arrayed as an aggregate of openings(a plurality of openings arrayed in the form of a square lattice, forexample) which are arrayed to be rotationally symmetrical (or axiallysymmetrical). The unit solid sections 12 c, each of which issubstantially surrounded by the plurality of openings 12 c, may besimilarly arranged.

[0144] Further, each liquid crystal domain is also preferably formed tobe rotationally symmetrical or axially symmetrical. Accordingly, it ispreferable that each opening 12 a and each unit solid section 12 c ineach liquid crystal domain are also rotationally symmetrical or axiallysymmetrical. More specifically, the display characteristics of theliquid crystal display device exhibit azimuth angle dependency, due tothe aligned state of the liquid crystal molecules (optical anisotropy).To reduce the azimuth angle dependency of the display characteristics,the liquid crystal molecules are preferably arranged with equalprobability for all azimuth angles. Further, it is more preferable thatthe liquid crystal molecules in each picture element region are alignedwith equal probability for all azimuth angles. Accordingly, the openings12 a are preferably of a shape that forms such a liquid crystal domainthat the liquid crystal molecules 30 a in each picture element regionare aligned with equal probability for all azimuth angles. Specifically,the opening 12 a is preferably formed to be rotationally symmetrical(preferably with a two or greater fold axis of symmetry) about itscenter (normal direction) as the symmetrical axis, and a plurality ofthe openings 12 a are preferably arranged to be rotationallysymmetrical. Further, the unit solid sections 12 c, each of which issubstantially surrounded by the openings 12 a, preferably has arotationally symmetrical shape, and the unit solid section 12 c ispreferably arranged to be rotationally symmetrical.

[0145] Note that, there are cases where a voltage is not sufficientlyapplied to the liquid crystal layer 30 in the vicinity of the center ofthe opening 12 a so that the voltage does not contribute to display inthis portion of the liquid crystal layer 30. In other words, there is acase where display quality is not impaired even when the liquid crystallayer 30 in the vicinity of the center of the opening 12 a has aslightly disturbed radially inclined alignment (even when the centralaxis does not exactly lie on the center of the opening 12 a, forexample). Thus, at least the liquid crystal domain corresponding to theunit solid section 12 c should be arranged to be rotationallysymmetrical or axially symmetrical.

[0146] Incidentally, the foregoing described the case where the liquidcrystal cell 100 is provided with the thin film transistor (TFT) as apixel element driving element (active element). However, an activeelement is not limited to this. For example, an MIM (Metal InsulatorMetal) element may be used as an active element for switching thepicture element electrode 12. Further, the liquid crystal display deviceis not limited to be of an active matrix type but may be of a simplematrix type. However, the active matrix liquid crystal display device,as in the present embodiment, can achieve display having higherdefinition and higher brightness compared with the simple matrix liquidcrystal display device, thereby realizing a liquid crystal displaydevice having good display quality.

[0147] Note that, the foregoing described the case where the liquidcrystal display device is of a transmissive type as an example. Howeverthe liquid crystal display device may be of a reflective type or of atransflective type. Further, even though the foregoing described thecase where the openings 12 a are formed in the picture element electrode12, the same effects can also be achieved when the openings are formedin the counter electrode 22.

[0148] As described above, a liquid crystal display device of thepresent invention is so arranged that d/p is set in a range between0.0021×(Vmax)²−0.0458×(Vmax)+0.65 and 0.0021×(Vmax)²−0.0458×(Vmax)+0.50,and that d·Δn/λ is set in a range between−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.124 and−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+1.7603, where d/p is theratio of a thickness d of a liquid crystal layer of a vertical alignmentmode with respect to the natural twist pitch p of a liquid crystal, Vmax[V] is the maximum applied effective voltage applied across the firstelectrode and the second electrode, and Δn is the refractive anisotropyof the liquid crystal layer.

[0149] With this arrangement, the liquid crystal layer has definedvalues of d/p and d·Δn/λ that reduce a quenching pattern to such adegree as to be unrecognizable for a user. Therefore, it is possible tosurely provide a liquid crystal display device capable of realizingbrighter display with higher display quality, compared with the casewhere the quenching pattern due to the liquid crystal molecules isrecognized.

[0150] The liquid crystal display device of the present inventionaccording to the foregoing arrangement may be so arranged that d·Δn/λ isset in a range between−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.041 and−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+1.891.

[0151] Further, the liquid crystal display device of the presentinvention according to the foregoing arrangement may be so arranged thatd/p is set in a range between 0.0021×(Vmax)²−0.0458×(Vmax)+0.63 and0.0021×(Vmax)²−0.0458×(Vmax)+0.53.

[0152] With these arrangements, since the liquid crystal layer hasdefined values of d/p and d·Δn/λ in the foregoing ranges, it is possibleto realize a liquid crystal display device capable of realizing evenbrighter display.

[0153] Further, the liquid crystal display device of the presentinvention may be so arranged that the liquid crystal layer includes apicture element region defined by the first electrode and the secondelectrode, the picture element region including at least one liquidcrystal domain in which liquid crystal molecules under applied voltageare aligned radially or in an axially symmetrical manner. Note that, thecenter of the radial alignment may or may not lie exactly on the centerof the liquid crystal domain. Alternatively, the liquid crystal displaydevice of the present invention may be so arranged that the liquidcrystal layer includes one or more picture element regions defined bythe first electrode and the second electrode, and the first electrodehas a portion that corresponds to the picture element region and inwhich one or more openings are formed, the opening and a solid section,which is a portion of the first electrode other than the opening, eachhaving a liquid crystal domain in which alignment directions of liquidcrystal molecules are controlled by an inclined electric field generatedfrom edge portions of the opening when a voltage is applied across thefirst electrode and the second electrode.

[0154] With these arrangements, the picture element region has theliquid crystal domain, and the liquid crystal molecules in the liquidcrystal domain are aligned radially or in an axially symmetrical manner.Thus, portions in the liquid crystal domain in which liquid crystalmolecules are respectively aligned in different directions can beoptically compensated for with one another. As a result, when the userviews the liquid crystal display device in any direction, the intensityof emergent light (picture element brightness) is substantially the sameover the entire picture element region, thereby realizing a liquidcrystal display device having good viewing angle characteristics.

[0155] Here, when the liquid crystal molecules are aligned radially orin an axially symmetrical manner, some of the liquid crystal moleculesare aligned such that their in-plane component coincides with thedirections of the polarization axes of the polarization plates. However,in the foregoing arrangement, the defined values of d/p and d·Δn/λ inthe foregoing ranges can avoid the quenching pattern due to the liquidcrystal molecules to a degree as to be unrecognizable for the user.Therefore, it is possible to realize a liquid crystal display devicehaving both good viewing angle characteristics and good display quality.

[0156] In particular, in the arrangement having the openings, the liquidcrystal domain formed on the opening and the liquid crystal domainformed on the solid section are formed by an inclined electric fieldgenerated from the edge portions of the openings. Therefore, the liquidcrystal domains are formed adjacent with each other, and the liquidcrystal molecules in the adjacent liquid crystal domains have asubstantially continuous alignment. As a result, a disclination line isnot formed between the liquid crystal domain formed on the opening andthe liquid crystal domain formed on the solid section, therebypreventing impairment of display quality. Further, since the alignmentof the liquid crystal molecules in the adjacent liquid crystal domainsis substantially continuous, high stability can be maintained for thealignment of the liquid crystal molecules.

[0157] Further, the liquid crystal display device of the presentinvention, when provided with an opening, may be so arranged that aplurality of the openings are provided in each of the picture elementregions, and the liquid crystal domain is formed for (i) each of theopenings and for (ii) each of one or more unit solid sections, which isa portion of the solid section surrounded by the openings.

[0158] With this arrangement, since a plurality of openings are providedfor each of the picture element regions, the openings can be sized to besmaller than the size when only a single opening is provided, providedthat the size of the picture element region is the same. This increasesthe area of the liquid crystal layer (viewed in a direction normal tothe substrate) that is directly influenced by the inclined electricfield. With this, it is possible to improve the optical characteristicsof the liquid crystal layer in response to an applied voltage(transmission intensity, for example), while improving the alignmentregulating forces on the liquid crystal molecules.

[0159] Further, the liquid crystal display device of the presentinvention may be so arranged that the openings are substantiallyidentical with one another in shape and size, and each of the openingsforms a unit lattice arranged to have rotational symmetry. For example,the openings may be arranged so that the center of each opening form asquare lattice. Note that, when the picture element region is dividedwith an opaque constituent member such as an auxiliary capacitance linefor example, the unit lattice should be arranged in each region thatcontributes to the display area.

[0160] With this arrangement, since the unit lattice is arranged to haverotational symmetry, a plurality of liquid crystal domains are arrangedwith high symmetry, with the unit lattice as a unit of symmetry. Thiscan improve the viewing angle dependency, which is one criteria ofdisplay quality. Further, by dividing the entire picture element regioninto unit lattices, the alignment of the liquid crystal layer can bestabilized over the entire picture element region.

[0161] Further, the liquid crystal display device of the presentinvention may be so arranged that at least one of the openings(typically, the opening that forms the unit lattice) has a rotationallysymmetrical shape. For example, each of the openings (when viewed in adirection normal to the substrate) may have a substantially circularshape, or a substantially regular polygonal shape (substantially squareshape, for example).

[0162] With these arrangements, since the opening has a rotationallysymmetrical shape, stability of the radially inclined alignment of theliquid crystal domain formed on the opening can be improved. Inparticular, when the opening is formed in a substantially circularshape, it is possible to further improve stability of the radiallyinclined alignment of the liquid crystal domain formed on the opening.

[0163] At least one of the unit solid sections may have a substantiallycircular shape. With this arrangement, it is possible to improvestability of the radially inclined alignment of the liquid crystaldomain formed on the unit solid section.

[0164] Note that, in either case, in each picture element region, a sumof the areas of the openings is smaller than the area of the solidsection on the first electrode. A larger area for the solid sectionincreases an area of the liquid crystal layer (viewed in a directionnormal to the substrate) that is directly influenced by the electricfield generated by the electrodes, thereby improving the opticalcharacteristics (transmission intensity, for example) of the liquidcrystal layer in response to an applied voltage.

[0165] For example, from the arrangement in which the opening has asubstantially circular shape and the arrangement in which the unit solidsection has a substantially circular shape, whichever arrangement thatincreases the area of the solid section is preferably selected. In thisway, the area of the liquid crystal layer (as viewed in a directionnormal to the substrate) that is directly influenced by the electricfield generated by the electrodes can be increased, thereby improvingthe optical characteristics (transmission intensity, for example) of theliquid crystal layer in response to an applied voltage. Typically, theopenings are preferably formed so that the solid section has asubstantially circular shape when the pitch of the unit lattice is notless than approximately 25 [μm], and that the opening has asubstantially circular shape when the pitch of the unit lattice is lessthan approximately 25 [μm].

[0166] At least one of the plurality of unit solid sections may have asubstantially rectangular shape with substantially arc-shaped corners.With this arrangement, it is possible to improve stability of theradially inclined alignment of the liquid crystal domain formed on theunit solid section, and to improve transmittance (effective apertureratio).

[0167] Further, the liquid crystal layer may have a dielectricanisotropy Δε in a range of from −2.5 to −6.5, and an elastic constantratio K11/K33 of from 0.9 to 2.0. This can further improve transmissionintensity when d/p and d·Δn/λ are set in the foregoing ranges, therebyrealizing a liquid crystal display device capable of realizing evenbrighter display.

[0168] Further, the liquid crystal display device of the presentinvention may be so arranged that the first electrode is made up of aplurality of picture element electrodes that respectively correspond toa plurality of the picture element regions, and the first substrateincludes an active element that is provided for each of the pictureelement regions so as to switch the first electrode.

[0169] With such an active matrix liquid crystal display device, it ispossible to realize display with higher definition and higher brightnesscompared with a simple matrix liquid crystal display device, therebyrealizing a liquid crystal display device having excellent displayquality.

[0170] Further, in the arrangement having the openings, it is possibleto realize stable radially inclined alignment only by providing theopenings for one of the pair of electrodes that face each other via theliquid crystal layer sandwiched therebetween. Therefore, it is possibleto manufacture the liquid crystal display device according to a knownmanufacturing method, only by modifying a photomask in such a mannerthat an opening having a desired shape is formed at a desired positionwhen patterning a conductive film into the picture element electrode.

[0171] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed:
 1. A liquid crystal display device having a firstsubstrate, a second substrate, and a liquid crystal layer between thefirst substrate and the second substrate, the liquid crystal displaydevice comprising: a first electrode provided on the first substrate;and a second electrode provided on the second substrate so as to facethe first electrode via the liquid crystal layer, the liquid crystallayer being vertically aligned when no voltage is applied across thefirst electrode and the second electrode, and the liquid crystal layerhaving a twisted structure and being aligned parallel to the substrateswhen a voltage is applied across the first electrode and the secondelectrode, said liquid crystal display device having a defined value ford/p between 0.0021×(Vmax)²−0.0458×(Vmax)+0.65 and0.0021×(Vmax)²−0.0458×(Vmax)+0.50, and said liquid crystal displaydevice having a defined value for d·Δn/λ between−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.124 and−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+1.7603, where d/p is aratio of a thickness d of the liquid crystal layer to a natural twistpitch p of a liquid crystal, Vmax [V] is a maximum applied effectivevoltage across the first electrode and the second electrode, and An is arefractive anisotropy of the liquid crystal layer.
 2. The liquid crystaldisplay device as set forth in claim 1, wherein: the defined value ofd·Δn/λ is between −0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+2.041 and−0.00026×(Vmax)³+0.016×(Vmax)²−0.2281×(Vmax)+1.891.
 3. The liquidcrystal display device as set forth in claim 1, wherein: the definedvalue of d/p is between 0.0021×(Vmax)²−0.0458×(Vmax)+0.63 and0.0021×(Vmax)²−0.0458×(Vmax)+0.53.
 4. The liquid crystal display deviceas set forth in claim 1, wherein: the liquid crystal layer includes apicture element region defined by the first electrode and the secondelectrode; and the picture element region includes at least one liquidcrystal domain in which liquid crystal molecules under applied voltageare aligned radially or in an axially symmetrical manner.
 5. The liquidcrystal display device as set forth in claim 1, wherein: the liquidcrystal layer includes one or more picture element regions defined bythe first electrode and the second electrode; and the first electrodehas a portion that corresponds to the picture element region and inwhich one or more openings are formed, the opening and a solid section,which is a portion of the first electrode other than the opening, eachhaving a liquid crystal domain in which alignment directions of liquidcrystal molecules are controlled by an inclined electric field generatedfrom edge portions of the opening when a voltage is applied across thefirst electrode and the second electrode.
 6. The liquid crystal displaydevice as set forth in claim 5, wherein: a plurality of the openings areprovided in each of the picture element regions; and the liquid crystaldomain is formed for (i) each of the openings and for (ii) each of oneor more unit solid sections, which is a portion of the solid sectionsurrounded by the openings.
 7. The liquid crystal display device as setforth in claim 6, wherein: the openings are substantially identical withone another in shape and size, and each of the openings forms a unitlattice arranged to have rotational symmetry.
 8. The liquid crystaldisplay device as set forth in claim 6, wherein: at least one of theopenings has a rotationally symmetrical shape.
 9. The liquid crystaldisplay device as set forth in claim 6, wherein: at least one of theopenings has a substantially circular shape.
 10. The liquid crystaldisplay device as set forth in claim 6, wherein: at least one of aplurality of the unit solid sections has a substantially circular shape.11. The liquid crystal display device as set forth in claim 6, wherein:at least one of a plurality of the unit solid sections has asubstantially rectangular shape with substantially arc-shaped corners.12. The liquid crystal display device as set forth in claim 6, wherein:a sum of areas of the openings in the picture element region is smallerthan an area of the solid section.
 13. The liquid crystal display deviceas set forth in claim 1, wherein: the liquid crystal layer has adielectric anisotropy Δε of from −2.5 to −6.5, and has an elasticconstant ratio K11/K33 of from 0.9 to 2.0.
 14. The liquid crystaldisplay device as set forth in claim 1, wherein: the first electrodecomprises a plurality of picture element electrodes that respectivelycorrespond to a plurality of the picture element regions; and the firstsubstrate includes an active element that is provided for each of thepicture element regions so as to switch the first electrode.